1. Field of the Invention
The present invention relates to an IR-reflecting laminated glass pane having an IR-reflective surface coating on a support film between two glass sheets.
2. Discussion of the Background
In particular, the invention relates to such laminated glass panes suitable as heat-protective panes for automobiles, as are disclosed, for example, in DE 2344616 A1, EP 0371949 A1, EP 0391165 A2, EP 0544717 B1, and U.S. Pat. No. 4,465,736, all of which are incorporated herein by reference in their entirety.
Such laminated glass panes, when subject to oblique incident light, frequently exhibit a disturbing optical quality defect or optical distortion, wherein the IR-reflecting surface does not appear uniform in reflection, but exhibits a shrinkage effect or even a hammering or wrinkling effect. This is well known and described in the literature. It is also known that this hammering effect is apparently the result of shrinkage of a support film and/or thermoplastic adhesive films during heating in the bonding process.
To reduce this annoying optical distortion, support films are proposed in U.S. Pat. No. 4,465,736 which have a very low degree of shrinkage.
In EP 0371949 A1, it is proposed that the aforementioned distortion be avoided by modifying the IR-reflecting surface coating so that reflection in the visible spectral range is limited to at most 2% and preferably less than 0.70%. Modification to the layer caused by shrinkage does indeed persist, but the shrinkage effect is then no longer visible to the eye to a disturbing extent.
EP 0544717 B1 attempts to solve this problem of optical distortion by incorporating special adhesive layers. According to this proposal, the polyvinyl butyral films to be used as special adhesive layers, have on the face in contact with the IR-reflecting coating a small, defined surface undulation pattern.
The prior art methods for avoiding the aforementioned optical distortion have specific disadvantages, and the problem of a hammering effect in laminated glass panes of this category has not been satisfactorily solved.